Isothermal Beta Grain Growth Kinetics of TC4-DT Titanium Alloy under Two Different Prior Processing Conditions: Deformed vs. Undeformed

Abstract

Abstract β grain growth kinetics of TC4-DT titanium alloy under two different prior processing conditions (deformed vs. undeformed) was investigated during isothermal heat treatments. Deformation was carried out in α+β two-phase field with deformation degree of 60% and air cooling. Heat treatment scheme with the temperatures above β transus temperature 10, 20, 30 °C and soaking time of 2, 5, 10, 30, 60, 120 min was used. The grain size parameters have been obtained by means of the image analysis software. Growth time exponent (n) and activation energy (Q) have been established for both conditions. For the undeformed samples, n varied in the range of 0.34∼0.35 and Q in the range of 86.8∼130 kJ·mol−1, while after deformation, the values of n and Q changed in the domain of 0.36∼0.39 and 76.6∼110 kJ·mol−1, respectively. Results show that the samples subjected to deformation exhibit higher growth time exponent and lower activation energy compared to the samples without deformation under the same heat treatment conditions. The variations of the growth time exponent with temperature and the activation energy with soaking time are ascribed to the interaction between diffusion of solute atoms and migration of grain boundaries both of which can be promoted by deformation. The influences of heating temperature, time and deformation on the uniformity of grain size were also studied and the intrinsic mechanism is attributed to the combined effect of β phase nucleation rate and β phase growth velocity under the above factors.